At the risk of sounding insulting or snobbish, the best investment you could make in that bike is a total replacement. The bike is very low line with obsolete components, dangerous steel rims and very poor brake levers. It was a cheap bike new and hasn't gotten any better with age. The expression; "throwing good money after bad" applies here.

If you have any interest in riding at all seriously, a better, newer, more competent bike is highly recommended. Then, and only then, invest in suitable tools to work on the newer bike. you needend spend a huge amount of money as good and appropriate used bikes are readily available on Craig's List or similar sources. I further recommend you have a knowledgeable friend go with you to assure whatever you buy is the proper size and suitable equipped.